Page 113 - Rollingbearings

Selecting grease or oil
Estimating the (centralized) greasing (Lubrication systems, As a rule, standard greases have a practical
relubrication interval page 120), you should choose oil instead. upper temperature limit of 100 °C (210 °F)
on the ring with the highest temperature.
Relubrication should occur frequently
for grease enough to avoid grease deterioration having Above this temperature, special greases or
an adverse effect on the bearing life. There- automatic (centralized) greasing systems
Lubricating grease slowly degrades and fore, the SKF relubrication interval, t , is should be used – otherwise, commonly the
f
therefore has a limited life. Grease life deined as the time period at the end of grease life would be too short.
depends on the operating conditions of the which there is only a 1% probability that the
bearing and the grease type. Rolling bearings bearing will fail because of grease degrad-
therefore have to be relubricated if: ation. This represents the L grease life. L
1
10
grease life represents a 10% probability failure
• the grease life is shorter than the speciied because of grease degradation. Grease life
bearing life depends mainly on:
• the grease becomes contaminated
• bearing type and size
It is important to calculate the grease • speed
relubrication interval and if it is unacceptably • load ratio C/P
short then, unless you use automatic • operating temperature
• grease type

Diagram 1
Process for selecting a suitable lubrication method for open bearings

Lubricant method selection

• Oil is used for other purpose(s)?
No Yes
• Need for heat removal by the lubricant?
Lubrication
• Other needs require oil lubrication?

B.4

Main grease selection criteria Main oil selection criteria
• Temperature range • Temperature range
• Consistency grade • Base oil viscosity
• Base oil viscosity • Additives
• Additives • Miscibility
• Miscibility

Oil lubrication

• Relubrication interval too short? Yes
• Grease consumption too high?

No

Grease lubrication

111